This invention relates to the use of metal soaps of polycarboxylic acids or polycarboxylic acid partial esters corresponding to general formula I EQU A--O--CO--X--CO--O--B (I)
in which
A and B together represent a metal ion from the group consisting of Mg.sup.2+, Ca.sup.2+ and Zn.sup.2+ or
A is alkyl or alkenyl containing 10 to 22 carbon atoms and B represents an equivalent of the metal ions from the group consisting of Mg.sup.2+, Ca.sup.2+ and Zn.sup.2+ and
X is an o-phenylene group, a group corresponding to general formula II EQU --CH(R.sup.1)--CH(R.sup.2)-- (II)
in which
R.sup.1 and R.sup.2 are selected from the group consisting of hydrogen, alkyl or alkenyl containing 10 to 22 carbon atoms and hydroxy,
a group corresponding to general formula III EQU --(CH.sub.2).sub.n -- (III)
in which n is the number 3 or 4, or a group corresponding to general formula IV EQU --CH.sub.2 --C(OH)(COOR.sup.3)--CH.sub.2 -- (IV)
in which
R.sup.3 represents alkyl or alkenyl containing 10 to 22 carbon atoms or an equivalent of the metal ions from the group consisting of Mg.sup.3+, Ca.sup.2+ and Zn.sup.2+,
with the provisos that
A is alkyl or alkenyl containing 10 to 22 carbon atoms and B is an equivalent of the metal ions from the group consisting of Mg.sup.2+, Ca.sup.2+ and Zn.sup.2+ where X is an o-phenylene group or a group corresponding to general formula II with R.sup.1 and R.sup.2 =hydrogen and/or hydroxy or X is a group corresponding to general formula III or IV and
A and B together form a metal ion from the group consisting of Mg.sup.2+, Ca.sup.2+ and Zn.sup.2+ where X is a group corresponding to general formula II in which at least one of the substituents R.sup.1 and R.sup.2 is alkyl or alkenyl containing 10 to 22 carbon atoms, as processing aids for polyesters.